The present invention relates to a suspension arrangement for a vehicle, and more particularly, but not exclusively to a suspension arrangement for an amphibious vehicle.
In conventional suspension arrangements a shock absorber or suspension strut is mounted at its upper end to a vehicle body, and at its lower end to a control arm of a vehicle wheel. The suspension strut usually consists of a cylinder and a shaft which telescopes within the cylinder, the cylinder and shaft being internally biased apart and damped. The cylinder is mounted on the control arm, and usually carries a seat for a coil spring. The coil spring is compressed between the seat and the vehicle body.
In more sophisticated vehicle suspension arrangements, it is known to mount a hydraulic cylinder at its upper end to a vehicle body and at its lower end to a control arm of a vehicle wheel. The cylinder is usually connected to an accumulator in the form of a reservoir of hydraulic oil, which is pressurised by compressed gas. The compressed gas provides resilience in the hydraulic system, and damping is provided by restrictions in the hydraulic lines.
It is often a requirement of an amphibious vehicle that the wheels of the vehicle can be retracted upwards and inboard of the vehicle body presenting a smooth hull surface for good marine performance. Conventional suspension arrangements do not allow for sufficient movement of a suspension strut or hydraulic cylinder without it interfering with the vehicle wheel being retracted.
Prior art retractable suspensions for amphibious vehicles include U.S. Pat. No. 5,690,046 (Grzech). This vehicle is an amphibious three-wheeled motorcycle, using hydraulic rams to withdraw coil spring and damper units on front and back wheels. The main drawback of this approach is that there is negligible camber change as the suspension operates, nor as the wheel is withdrawn. With the relatively small wheels disclosed, this is not a problem, because the wheels can be stored vertically within the vehicle bodywork. However, such small wheels limit both on-road ground clearance, and the deadrise (the depth of the “vee” in lateral cross-section) on an amphibious vehicle hull. This in turn limits marine speed and handling potential. It should also be noted that the vehicle would have to bank into turns on the road, and to use motorcycle tyres, to obtain adequate roadholding without wheel camber change on corners. This is therefore not a suitable solution for a car-sized amphibian.
WO 95/23074 (Roycroft) discloses rotating torsion bars which lift road wheels. This is an elegant solution, but takes up a lot of space away from the wheels, in the centre of the vehicle. Similarly, U.S. Pat. No. 5,755,173 (Rorabaugh and Costa) discloses a system using lateral screw jacks, which pass across the centre of the vehicle adjacent to front and rear axles; which could again cause packaging problems. It is generally accepted in automotive engineering that it is advantageous to contain wheel suspensions entirely within the respective wheel arches; which is one reason why both torsion bar and leaf spring suspensions have fallen out of favour.
It is therefore an object of the invention to provide an improved suspension arrangement, which provides for increased upward and inboard movement of a vehicle wheel being retracted.